The major clinical symptom of metastatic medullary thyroid carcinoma is diarrhea; occasionally a patient will have flushing episodes.

RET is involved in the regulation of cell growth and development and its germline mutation is responsible for nearly all cases of hereditary or familial medullary thyroid carcinoma.

[citation needed] Seventy-five percent of medullary thyroid carcinoma occurs in individuals without an identifiable family history and is assigned the term "sporadic".

Approximately 25-60% of sporadic medullary thyroid carcinomas have a somatic mutation (one that occurs within a single "parafollicular" cell) of the RET proto-oncogene.

A recent Cochrane systematic review assessed the diagnostic accuracy of basal and stimulated calcitonin for Medullary Thyroid Carcinoma.

A plasma level of metanephrines should be checked before surgical thyroidectomy takes place to evaluate for the presence of pheochromocytoma since 25% of people found to have medullary thyroid cancer have the inherited form from the MEN2A syndrome.

[citation needed] A total thyroidectomy with bilateral neck dissection is the gold standard for treating medullary thyroid cancer, and is the most definitive means of achieving a cure in patients without distant metastases or extensive nodal involvement.

Extensive surgery can be effective when the condition is detected early, but a risk for recurrence remains, particularly in patients with multiple positive lymph nodes or extracapsular invasion.

In lower risk cases surgery may be delayed up to the age of ten years, the precise timing depending on the mutation and other factors.

[citation needed] External beam radiotherapy is recommended when there is a high risk of regional recurrence, even after optimum surgical treatment.

The authors of the study [14] wrote: "in 40 high risk patients (microscopic residual disease, extraglandular invasion, or lymph node involvement), the local/regional relapse free rate was 86% at 10 years with postoperative external beam radiation (25 patients), and 52% for those with no postoperative external radiation (p = 0.049).

To optimize local/regional tumor control, we therefore continue to advise external beam radiation in patients at high risk of local/regional relapse.

The major side effects of this class of drug include hypertension, nausea, diarrhea, some cardiac electrical abnormalities, and thrombotic or bleeding episodes.